The Prophet [SAW] forbade mixing Az-Zahuw and dried dates, and mixing Al-Busr and dried dates, and he said: "Soak each one of them on its own in vessels that are tied shut."  

أَنَّ النَّبِيَّ ﷺ نَهَى عَنْ خَلِيطِ الزَّهْوِ وَالتَّمْرِ وَخَلِيطِ الْبُسْرِ وَالتَّمْرِ وَقَالَ لِتَنْبِذُوا كُلَّ وَاحِدٍ مِنْهُمَا عَلَى حِدَةٍ فِي الأَسْقِيَةِ الَّتِي يُلاَثُ عَلَى أَفْوَاهِهَا